Boilers are classified into two distinct types commonly known as fire tube and water tube boilers. A fire tube boiler transfers heat to the water by moving hot gases along the inside of small tubes in a controlled path. The water is in a large mass and, except for natural convection forces, the water is stationary. A water tube boiler transfers heat by confining the water in small tubes which causes the water to flow rapidly upwards, creating controlled rapid water circulation. The hot gases are not controlled to any absolute specific path. Fire tube boilers are the more economical type up to 20,000 pounds of steam per hour capacity whereas water tube boilers are the more economical for capacities over 20,000 pounds of steam per hour.
Both boiler types are designed to run at a fuel to water efficiency of 80 percent. To obtain higher efficiencies both types of boilers must go to expensive additional equipment and these decisions are usually made on a job-by-job basis, depending on the particular application.
Numerous designs exist but it is an object of the present invention to provide one which is simple to construct, assemble and operate, which is highly efficient and capable of handling varying loads, and which is suitable for use on large scale as in large buildings, industrial electric and co-generation plants as well as in relatively small residential installations.
These objects are realized in accordance with the present invention pursuant to which there is provided a boiler comprising a housing having a top provided with a gas outlet, bottom, left and right sides and a front and back, and within the housing an upper manifold and lower manifold or manifolds substantially parallel to the top, bottom and side walls, two sets of tubes, each set comprising a plurality of tubes, one set joining the upper left side of the manifold to the lower left side of the manifold and the other set joining the upper right side of the manifold to the lower right of the manifold, the tubes of each set rising from their lower manifold upwardly along their respective side wall, crossing the housing to the opposite side wall, re-crossing the housing to their respective side wall, rising there along and eventually joining their upper manifold, the horizontal runs of the tubes of one set being vertically offset relative to the horizontal runs of the tubes of the other set so as to form a plurality of superposed chambers, at least one tube of each set being differently bent from the others of that set so as to form access openings from each chamber to the chambers above and below, the openings from chamber to chamber being offset so as to require a gas flowing through said chambers to traverse one chamber from front to back and the next chamber from back to front, means for introducing liquid into one of the manifolds and for withdrawing the liquid from the outer manifold, and means for introducing a combustion gas into the lowermost of the superposed chambers, the combustion gas rising successively through the chambers which is successively and alternately traverses from front to back and then from back to front until it exits from the uppermost chamber through the gas outlet in the top, liquid flowing through the manifolds and tubes being heated by the combustion gas.
Advantageously, the tubes of each set are in substantial contact with one another so as substantially to prevent passage of combustion gas there between. In a preferred embodiment there is provided at least one baffle within at least one of the chambers extending from top to bottom and from one of the sides toward but terminating short of the other side, whereby combustion gas traversing that chamber from front to back is additionally forced to flow laterally to get around said baffle.
The boiler meets all of the requirements of the American Society of Mechanical Engineers boiler and pressure vessels, sections I and IV, which are recognized by agencies of most governments. The novel boiler incorporates the best features of the fire tube boiler by controlling the passage of hot gases and, by confining the water within small tubes, takes advantage of the best features of the water tube boiler.
All internal parts and surfaces are easily accessible for service and cleaning so the unit is suitable for burning light oil, residual oils, crude oils, waste oils, any type of gas, any type of coal or solid fuel including municipal waste.